1. Field of the Invention
This invention relates in general to an automotive type internal combustion engine and more particularly to a control device for variably controlling a purge of fuel vapors from a storage canister into the engine.
2. Prior Art
Carbon canister storage systems are known for storing fuel vapors emitted from an automotive-type fuel tank to prevent emission into the atmosphere of evaporative fuel components. These systems usually include a canister containing activated carbon with an inlet from the fuel tank or other reservoir. When the fuel vaporizes, the vapors will flow either by gravity or under vapor pressure into the canister to be adsorbed by the carbon inside. Filling the fuel tank with fuel may displace fuel vapors in the fuel tank and drive them into the canister. Subsequently, in most instances, the purge line connected from the canister outlet to the carburetor or engine intake manifold purges the stored vapors into the engine during engine operation. The canister contains a purge fresh air inlet to cause a sweep of the air across the carbon particles to thereby desorb the carbon of the fuel vapors.
In most instances, a purge or nonpurge of vapors is an on/off type of operation. That is, either the purge flow is total or zero. For example, U.S. Pat. No. 3,831,353 to Toth teaches a fuel evaporative control system and associated canister for storing fuel vapors and subsequently purging them back into the engine air cleaner. However, there is no control valve mechanism to vary the quantity of purge flow. As soon as the throttle valve is open, the fuel vapors are purged continuously into the manifold.
U.S. Pat. No. 4,326,489 to Heitert teaches a fuel vapor purge control device that controls a vacuum servo mechanism connected to a valve member that is slidable across a metering slot to provide a variable flow area responsive to changes in engine intake manifold vacuum to accurately meter the re-entry of fuel vapors into the engine proportionate to engine airflow.
U.S. Pat. Nos. 4,013,054; 4,275,697; 4,308,842; 4,326,489 and 4,377,142 disclose fuel purging systems incorporating some form of air/fuel ratio control but include no provision for applying a sequence of time varying pulses to the solenoid purge control valve.
As described, typical onboard refueling vapor recovery systems use an activated carbon canister to store the gasoline vapors which are displaced when refueling of the vehicle is performed. These vapors are subsequently purged from the system into the engine by passing air into the canister. This causes a potential enrichment of the engine's air/fuel ratio and an increase in the engine's emissions, such as carbon monoxide and hydrocarbon.
Such undesirable effects of purging can be reduced with present day fuel systems which employ feedback from an EGO sensor in the engine's exhaust to regulate the air/fuel ratio. Unfortunately, air/fuel ratio feedback cannot instantaneously reduce the air/fuel perturbations which result from abrupt changes in purging because of the inherent propagation time through the engine and exhaust system. As a result, there will always be short periods of uncontrolled air/fuel perturbations whenever the refueling vapor purge flow changes abruptly, such as at the beginning or end of a purge command signal. An abrupt increase of a vapor filled purge, such as that from a vapor filled canister, can cause an undesirably rich air fuel ratio. On the other hand, an abrupt decrease with a substantially air filled purge, such as that from a vapor free canister, can also cause an undesirably rich air fuel ratio.
There still remains a need to control the purge flow into the engine so that desirable engine operating conditions, such as the air/fuel ratio, are maintained and control of emissions from the engine is maintained within desirable limits. These are some of the problems this invention overcomes.